Recently, solder materials that do not contain Pb, such as Sn—Cu eutectic solder and Sn—Ag eutectic solder, have been actively developed so as to replace known Sn—Pb solder as a solder material used for mounting electronic components, in consideration of the environment.
For example, Patent Document 1 discloses solder including Cu balls and Sn balls wherein a compound containing Cu6Sn5 is formed by the Sn balls and some of the Cu balls at a temperature equal to or higher than the melting point of Sn, and the Cu balls are bonded to each other by the compound containing Cu6Sn5.
Patent Document 1 discloses Sn—Cu eutectic solder paste in which a first metal powder 104 prepared by forming a Sn film 103 on the surfaces of Cu balls (powder) 102 by plating and Sn balls (powder) 105 are dispersed in a flux 106, as shown in FIG. 6.
According to Patent Document 1, and as shown in FIG. 7, solder paste 101 is applied on a conductive part of a printed circuit board 107, and a chip-type electronic component 108 such as a monolithic ceramic capacitor is then mounted thereon. When a reflow treatment is then performed at a temperature of 250° C. or higher, the Sn component (derived from the plated films and the Sn powder) is melted. The Cu balls 102 is wetted and dispersed in the molten Sn component, and the Cu balls 102 is uniformly diffused in the flux 106 to form an intermetallic compound 109 composed of Cu6Sn5, as shown in FIG. 8. Accordingly, the printed circuit board 107 and the electronic component 108 are electrically bonded, with solder 110 therebetween.    Patent Document 1: Japanese Patent No. 3558063